The present invention relates to porous membranes for coating absorptive materials and processes for their production.
There is considerable demand for articles which are absorbent, examples-of such articles being sanitary pads, nappies, plasters and wound dressings in general.
Many materials are suitable for use in such absorbent articles, and these generally comprise an interlinked, or cross-linked, disperse layer of a fibrous substance, such as cellulose, which has been so treated as to be able to absorb liquids. For example, EP-A-252650 discloses a material made of stiffened curled cellulosic fibers, while EP-A-7134 discloses a fibrous cellulosic sheet, the fibers being bibulous cellulosic fibers and/or sodium carboxymethyl cellulose fibers. These are cross-linked by wetting and applying heat and pressure.
For some applications, it is suitable to apply the material directly to the area where it is required to absorb liquid, but this, as a rule, is undesirable for the treatment of wounds, as the fibers may irritate, or penetrate the wound, or both. In addition, exposed fibrous matrices, especially those containing wound exudates, can provide an ideal environment for the reproduction of bacteria.
To overcome such problems, articles comprising such materials generally further comprise protective membranes. In such instances, it is common to have an impervious membrane on the side of the material not intended for absorption, while a porous membrane is provided on the absorptive side. Well known examples of this type of application include nappies and sticking plasters.
Whilst it is relatively easy to provide a porous membrane to allow the cross passage of liquids, problems arise in preventing backflow of the liquids. In sticking plasters, for example, the porous membrane characteristically comprises an impervious plastics film with many small perforations.